Population Projections Program PD. Projections of the total resident population by 5-year age groups,
and sex with special age categories: 1999 to 2050. Washington, DC: US Census Bureau; January 13, 2000.

Hollman FW, Mulder TJ, Kallan JE. Methodology and Assumptions for the Population Projections
of the United States: 1999 to 2100. Washington, DC: Population Projections Branch, Population Division,
US Census Bureau, Dept of Commerce; January 13, 2000. Working Paper No. 38.

Context Atrial fibrillation is the most common arrhythmia in elderly persons
and a potent risk factor for stroke. However, recent prevalence and projected
future numbers of persons with atrial fibrillation are not well described.

Objective To estimate prevalence of atrial fibrillation and US national projections
of the numbers of persons with atrial fibrillation through the year 2050.

Design, Setting, and Patients Cross-sectional study of adults aged 20 years or older who were enrolled
in a large health maintenance organization in California and who had atrial
fibrillation diagnosed between July 1, 1996, and December 31, 1997.

Main Outcome Measures Prevalence of atrial fibrillation in the study population of 1.89 million;
projected number of persons in the United States with atrial fibrillation
between 1995-2050.

Results A total of 17 974 adults with diagnosed atrial fibrillation were
identified during the study period; 45% were aged 75 years or older. The prevalence
of atrial fibrillation was 0.95% (95% confidence interval, 0.94%-0.96%). Atrial
fibrillation was more common in men than in women (1.1% vs 0.8%; P<.001). Prevalence increased from 0.1% among adults younger than
55 years to 9.0% in persons aged 80 years or older. Among persons aged 50
years or older, prevalence of atrial fibrillation was higher in whites than
in blacks (2.2% vs 1.5%; P<.001). We estimate
approximately 2.3 million US adults currently have atrial fibrillation. We
project that this will increase to more than 5.6 million (lower bound, 5.0;
upper bound, 6.3) by the year 2050, with more than 50% of affected individuals
aged 80 years or older.

Conclusions Our study confirms that atrial fibrillation is common among older adults
and provides a contemporary basis for estimates of prevalence in the United
States. The number of patients with atrial fibrillation is likely to increase
2.5-fold during the next 50 years, reflecting the growing proportion of elderly
individuals. Coordinated efforts are needed to face the increasing challenge
of optimal stroke prevention and rhythm management in patients with atrial
fibrillation.

Atrial fibrillation is the most common clinically significant cardiac
arrhythmia. It is also a potent risk factor for ischemic stroke, increasing
the risk of stroke 5-fold and accounting for approximately 15% of all strokes
nationally.1 Symptomatic atrial fibrillation
may also reduce quality of life, functional status, and cardiac performance.2 It is associated with higher medical costs as well
as an increased risk of death.3 Specifying
the prevalence of atrial fibrillation in the United States has important implications
for understanding the population burden of disability and medical costs associated
with this arrhythmia.

The prevalence of atrial fibrillation increases substantially with age.4 Several previous studies have reported varying estimates
of the prevalence of atrial fibrillation ranging from 1.2% to 2.8% in persons
aged 60 through 69 years to 7.3% to 13.7% in persons aged 80 years or older.5- 8 However,
these studies have been limited by relatively small numbers of individuals
with atrial fibrillation,5- 8
restricted age ranges,8 ethnically homogeneous
samples,5- 7 and
potentially biased ascertainment of atrial fibrillation by reliance on hospitalization
data or patient self-report for the detection of atrial fibrillation.6- 8 Overall, these limitations
may reduce the generalizability of prior studies' results to current populations.

We assembled a contemporary cohort of patients with atrial fibrillation
to provide age-, sex-, and race-specific period prevalence estimates of atrial
fibrillation among adults and to project the number of persons in the United
States who will have atrial fibrillation through the year 2050.

Methods

Study Population

We assembled a cohort of adults aged 20 years or older with diagnosed
atrial fibrillation between July 1, 1996, and December 31, 1997, who received
care within Kaiser Permanente of Northern California, a large group-model
health maintenance organization. Kaiser Permanente cared for nearly 3 million
members during the study period. Health plan members had a demographic, race
or ethnic, and socioeconomic profile similar to the overall northern California
population, with the exception of a lower proportion of patients aged 65 years
or older (15% vs 17%) and only slightly higher median incomes (35% vs 42%
with <$35 000 annual household income) (N. P. Gordon, ScD, unpublished
data, July 2000).

To identify patients with atrial fibrillation, we searched an automated
clinical database containing diagnoses from all ambulatory visits for a diagnosis
of atrial fibrillation (code 427.31 from the International
Classification of Diseases, Ninth Revision, Clinical Modification [ICD-9]), an electrocardiographic database for physician-confirmed
diagnoses of atrial fibrillation, and an automated hospital discharge diagnosis
database for principal discharge diagnoses of atrial fibrillation (ICD-9 code 427.31). Of note, the electrocardiographic database included
diagnoses for all inpatient and outpatient electrocardiograms (Model No. XLi;
Hewlett Packard; Boise, Idaho), which have been performed in all Kaiser Permanente
medical centers since 1994.

We applied several exclusion criteria to identify only adult patients
with nontransient atrial fibrillation who were also health plan members to
ensure that they were in the source population for prevalence calculations.
Thus, exclusion criteria included presumed transient atrial fibrillation identified
only by an electrocardiogram performed during a hospitalization without a
principal discharge diagnosis of atrial fibrillation, transient atrial fibrillation
after recent cardiac surgery, no evidence of health plan membership surrounding
the atrial fibrillation diagnosis, age younger than 20 years on the index
date, and hyperthyroidism during the 12 months before the index atrial fibrillation
diagnosis. We captured diagnoses for exclusion criteria from comprehensive
hospital discharge diagnosis and billing claims databases for health plan
and out-of-network admissions, respectively, as well as an automated ambulatory
database of emergency department and outpatient clinic visits.

Transient, perioperative atrial fibrillation was defined as the presence
of a single diagnosis of atrial fibrillation within 30 days after coronary
artery bypass graft surgery (ICD-9 codes 36.10-36.19),
pericardial surgery (ICD-9 37.10-37.12, 37.24-37.25,
37.31-37.33, 37.35, or 37.40), or structural cardiac repair surgery (ICD-9 35.31-35.39, 35.41, 35.42, 35.50-35.54, 35.60-35.63,
or 35.70-35.73) and no evidence of atrial fibrillation in our databases subsequently.
Concomitant hyperthyroidism was defined as an outpatient or hospital discharge
diagnosis of hyperthyroidism or thyrotoxicosis (ICD-9
242.0-242.9), a filled prescription for methimazole or propylthiouracil in
the outpatient pharmacy database, and/or a low serum thyroid-stimulating hormone
level found in a laboratory database (without a concurrent prescription for
thyroxine) during the 12 months before the index atrial fibrillation diagnosis.

Patient Characteristics

Patient age, sex, and race or ethnicity (white, black, Hispanic, and
other or multiple) were ascertained from administrative and hospitalization
files. Race or ethnicity status was available on 89% of the cohort. We searched
inpatient and outpatient databases during the 5 years before index date to
identify diagnosed valvular heart disease, which was defined as mitral stenosis,
a prosthetic heart valve, or evidence of mitral and/or aortic valve repair
or replacement (ICD-9 codes 35.01-35.02, 35.11-35.12,
35.21-35.24, 394.0, 394.2, 396.0, 396.1, 396.8, 746.5, V42.2, or V43.3); previous
ischemic stroke (ICD-9 433-434); previously diagnosed
heart failure (ICD-9 402.01-402.11, 402.91, 425.1,
425.4, 425.5, 425.7, 425.9, or 428.0-428.9), and known coronary heart disease
(ICD-9 codes 410-414). We relied on an ambulatory
visit database to identify diagnosed hypertension (ICD-9 401-405). The presence of diabetes mellitus was assessed from a longitudinal
health plan diabetes registry9 that identified
patients with diabetes between 1994-1997 using relevant inpatient and outpatient
diagnoses (ICD-9 250.0-250.8), self-reported diabetes
from a patient survey, an abnormal (>6.7%) hemoglobin A1C level,
or a filled prescription for oral hypoglycemic agents or insulin.

Prevalence of Atrial Fibrillation

We calculated the period prevalence of atrial fibrillation in the adult
population within Kaiser Permanente of Northern California overall and stratified
by age and sex.10 The denominator for the prevalence
calculations was the adult (age ≥20 years) population of health plan members
during the study period. This was determined by taking the average number
of registered adult members from July 1, 1996, through December 31, 1997,
based on quarterly membership counts from administrative files. Based on an
a priori hypothesis,11 we attempted to compare
the prevalence of atrial fibrillation between white and black patients. The
proportion of white and black subjects in each 5-year age-sex subgroup 50
years or older in the source population was estimated using self-reported
race or ethnic data from a weighted sample of 11 047 Kaiser Permanente
members 50 years and older (N. P. Gordon, ScD, unpublished data, July 2000).
Only those whose race or ethnicity were known and were 50 years and older
were included in comparisons of the prevalence of atrial fibrillation between
white and black patient subgroups.

United States Projections of Atrial Fibrillation

We applied the age- and sex-specific prevalence calculations of atrial
fibrillation in our study population to 1995 United States census data12 to estimate the number of US adults with this condition
in 1995. Based on the anticipated growth of the population in the United States,
we projected the number of adults who will have diagnosed atrial fibrillation
by directly applying age- and sex-specific prevalence estimates from our study
to US Census projections for each adult age and sex category through the year
2050.12,13 We also conducted a
sensitivity analysis of our projections using different assumptions of the
prevalence of atrial fibrillation and US Census projections. Specifically,
we used the 95% confidence intervals (CIs) of the age- and sex-specific prevalence
of atrial fibrillation from our study to create low and high scenarios for
its prevalence in the population. We also used the reasonable low and reasonable
high series from US Census projections,12,13
which correspond to an approximate 10% lower or higher estimate, to reflect
the potential error in the census projection. By combining these assumptions,
we established a lower and upper bound of our projections of the number of
US adults who would have atrial fibrillation.

Statistical Analysis

Continuous variables are presented as mean (SD), and categorical variables
are reported as proportions with 95% CIs.10
Estimates of the period prevalence of atrial fibrillation are presented as
proportions with 95% CIs. Prevalence between subgroups was compared using
a χ2 test. As noted above, the projected numbers of adults
with atrial fibrillation in the United States are reported per 5-year period
between 1995 and 2050 with a sensitivity analysis based on varying assumptions
of atrial fibrillation prevalence and US Census estimates.

Results

Cohort Assembly

During the study period, we initially identified 21 634 patients
with suspected nontransient atrial fibrillation based on 1 or more of the
following methods, which were not mutually exclusive: 15 570 with 1 or
more outpatient diagnoses of atrial fibrillation; 13 052 patients with
at least 1 electrocardiogram showing atrial fibrillation in the electrocardiographic
database; and 1434 with a principal hospital discharge diagnosis of atrial
fibrillation (Figure 1). We excluded
1826 patients with atrial fibrillation that was detected only by an electrocardiogram
during a hospitalization whose principal discharge diagnosis was not atrial
fibrillation, 1829 patients without health plan membership, 70 patients who
were younger than 20 years on the index date, 108 patients with presumed transient
perioperative atrial fibrillation following cardiac surgery, and 350 patients
with evidence of recent hyperthyroidism. The final cohort included 17 974
adult patients with diagnosed, presumed nontransient atrial fibrillation.

Within this cohort, 25% were identified only by more than 1 outpatient
diagnosis of atrial fibrillation during the study period; 18% were identified
only by a single outpatient diagnosis of atrial fibrillation during the study
period. We validated the approach of including these patients in the cohort
by searching the medical records for electrocardiograms in a random sample
of patients from each group. In the sample of 50 patients identified by more
than 1 outpatient atrial fibrillation diagnosis only, 78% had at least 1 electrocardiogram
in their medical record showing atrial fibrillation. Fifty-six percent of
the sample of 50 patients identified only by a single outpatient atrial fibrillation
diagnosis had a corresponding electrocardiogram with atrial fibrillation in
their records. Essentially all of the retrieved electrocardiograms showing
atrial fibrillation had been performed before the start of the electrocardiographic
database in 1994. Taking these validation results together with the other
subjects identified using electrocardiographic and principal discharge diagnoses,
we estimate that at least 87% of the entire cohort had electrocardiographically
confirmed atrial fibrillation.

Patient Characteristics

The mean (SD) age of the cohort was 71.2 (12.2) years, and 43.4% were
women. Ten percent of the cohort were younger than 55 years; 13.6%, 55 through
64 years; 31.9%, 65 through 74 years; 34.1%, 75 through 84 years; and 10.5%,
85 years or older. Other characteristics of the cohort are summarized in Table 1. Of note, only 5% had known valvular
heart disease.

Prevalence of Atrial Fibrillation

Among the 1.89 million adult health plan members during the study period,
the overall prevalence of diagnosed atrial fibrillation was 0.95% (95% CI,
0.94%-0.96%). The prevalence of atrial fibrillation increased with older age
(Figure 2), ranging from 0.1% among
persons younger than 55 years to 9.0% among patients 80 years or older; among
persons 60 years or older, 3.8% had atrial fibrillation.

The prevalence of atrial fibrillation was greater in men than in women
overall (1.1% vs 0.8%, P<.001) and in every age group. In women, the prevalence
increased from 0.1% among those younger than 55 years to 9.1% among those
85 years or older (Figure 2). In
men, the prevalence of atrial fibrillation ranged from 0.2% in those younger
than 55 years to more than 11% among those 85 years or older (Figure 2).

In addition, among patients 50 years or older, atrial fibrillation appeared
to be more common in white (2.2%) than in black (1.5%, P<.001) patients. We found that the prevalence of atrial fibrillation
was similar in white (0.5%) vs black (0.5%) patients aged 50 through 59 years
(P = .51) but was more common in white vs black patients
in the following age groups, respectively: 60 through 69 years, 1.8% vs 1.3%
(P = .001); 70 through 79 years, 5.2% vs 4.4% (P = .003); and 80 years and older, 9.9% vs 7.7% (P = .001).

United States Projections of Atrial Fibrillation

We next applied the age- and sex-specific prevalence data from our study
population to census information on the US population12,13
to estimate the number of adults with atrial fibrillation through the year
2050 (Figure 3). We estimate that
approximately 2.1 million Americans had atrial fibrillation during the period
of cohort assembly and that there are nearly 2.3 million US adults with atrial
fibrillation currently (lower bound, 2.0 million; upper bound, 2.5 million).
Furthermore, we project that this number will increase approximately 2.5-fold
to more than 5.6 million by the year 2050 (lower bound, 5.0 million; upper
bound, 6.3 million) (Figure 3).
As the overall number of persons affected by atrial fibrillation increases,
the proportion of the most elderly will similarly increase. We estimate that
currently 1.85 million (82%) of US adults with atrial fibrillation are 65
years or older and nearly 830 000 (37%) are 80 years or older (Table 2). By the year 2050, we project
that 4.97 million (88%) of US adults with atrial fibrillation will be 65 years
or older and 2.95 million (53%) will be 80 years or older. Of note, despite
the higher prevalence among men, we estimate that about half of adults with
atrial fibrillation will be women, reflecting the greater number of older
women in the United States. Furthermore, given the decline in the incidence
of rheumatic fever within the United States and the relatively low prevalence
of known valvular heart disease observed in our cohort (4.9%), the overwhelming
majority of these patients will have nonvalvular atrial fibrillation.

Comment

Within a large, ethnically diverse population, we found that 1% of all
adults were diagnosed with atrial fibrillation. The prevalence of atrial fibrillation
was strongly associated with increasing age, with nearly 4% of persons 60
years and older and 9% of persons 80 years and older having been diagnosed
with atrial fibrillation. Women had a lower prevalence of atrial fibrillation
at every age compared with men, but the overall number of affected women was
similar. Black patients appeared to be less likely than white patients to
have atrial fibrillation. The national impact of this arrhythmia is substantial,
because we estimate that 2.3 million US adults currently have atrial fibrillation.
This burden will likely increase in the coming decades since we project that
5.6 million US adults will have atrial fibrillation by the year 2050. This
nearly 2.5-fold estimated increase reflects the projected increase in the
number of elderly persons, mostly resulting from the higher birth rate during
the immediate post-World War II era. Indeed, we estimate that there will likely
be nearly 3 million individuals 80 years or older with atrial fibrillation
by the year 2050.

Our study had several strengths. We assembled the largest cohort of
adults with atrial fibrillation reported to date—many times the size
of prior studies of atrial fibrillation prevalence4—which
allowed a relatively precise estimation of recent age-, sex-, and race-specific
prevalence of diagnosed atrial fibrillation within an unselected, usual care
population. We estimate that at least 87% of this cohort had electrocardiographically
confirmed atrial fibrillation. Our cohort was highly representative of the
California state population and had greater representation of older patients,
particularly those 80 years and older, as well as women compared with earlier
randomized trial populations.1 Our cohort also
had greater race or ethnic diversity than randomized trial populations and
most observational studies.1,5- 8
Finally, our estimates of atrial fibrillation prevalence are the most current
assessments to date.

Five previous studies have provided age-specific prevalence estimates
based on at least 75 cases of atrial fibrillation.5- 8,14
Our finding that the prevalence of atrial fibrillation increases substantially
with age, especially after age 50 years, is consistent with these studies,
but the point estimates varied markedly among these studies. For example,
among patients aged 75 through 79 years, we found a prevalence of 6.0% compared
with a range of 4.8% to 13.7% in other studies5- 8,14
although the CIs from these latter studies' estimates were wide. In addition
to random variation, these differences may be explained, in part, by variation
in the populations studied and the methods used to detect atrial fibrillation.
The approaches used to identify atrial fibrillation varied substantially across
studies and included medical record review only7;
triennial patient surveys6; a single screening
electrocardiogram and physical examination among potential trial participants14; a single-screening electrocardiogram and/or self-reported
atrial fibrillation from recruited subjects8;
and biennial screening electrocardiograms, surveys, physical examinations,
and medical records review from recruited subjects.5
Interestingly, despite using automated clinical and electrocardiographic databases
to identify atrial fibrillation within the context of usual clinical care
in our population, our prevalence estimates are most consistent with those
of the Framingham Heart Study,5 which used
the most systematic screening methods (ie, biennial surveys, physical examinations,
electrocardiograms, and medical records review of hospitalizations and outside
physician visits) to detect atrial fibrillation among a recruited prospective
cohort. However, our study demonstrates a broader range of age-specific prevalences
in a more ethnically diverse and contemporary population.

Our preliminary finding that atrial fibrillation was less prevalent
among older black patients than white patients is consistent with a previous
report from a cohort of older adults.11 However,
our estimates are limited because race or ethnicity status was missing in
11% of patients with atrial fibrillation and was determined for the source
population from survey results in a sample of health plan members. Additional
research in other populations is needed to confirm this finding and if confirmed
to explore underlying mechanisms.

Our study also had several limitations. It is likely that we missed
some patients with atrial fibrillation. In patients with asymptomatic atrial
fibrillation, which occurs more frequently than what has been previously estimated,15,16 or paroxysmal atrial fibrillation,
the only way to detect the arrhythmia would be through frequent repeated electrocardiograms
(which would depend on atrial fibrillation being present at the time of the
test) or continuous 24-hour ambulatory electrocardiographic monitoring. Neither
of these options is feasible for such a large population. However, the similarities
between our prevalence estimates and those from previous studies suggest that
we are not missing a large number of cases. We may have misclassified some
patients whose atrial fibrillation was based solely on outpatient physician
diagnoses; however, our validation studies suggest that at least 87% of the
cohort had atrial fibrillation confirmed electrocardiographically. We were
also unable to delineate the prevalence of chronic permanent vs paroxysmal
atrial fibrillation. Our US projections were necessarily limited to the assumptions
of the underlying census projections17 and
do not adjust for potential future changes in associated conditions such as
hypertension and heart failure. Given these caveats, our estimates of the
numbers of patients with atrial fibrillation in the future may prove conservative.

In conclusion, atrial fibrillation affects 1 in 25 adults 60 years or
older and nearly 1 in 10 adults 80 years or older. Atrial fibrillation confers
a large burden from symptoms and ischemic stroke on elderly patients presently,
and its impact will be amplified as the number of individuals with atrial
fibrillation increases nearly 2.5-fold over the next 50 years. Coordinated
efforts by cardiologists, primary care providers, and neurologists will be
needed to meet the increasing challenge of stroke prevention and rhythm management
in the growing elderly population with atrial fibrillation.

Population Projections Program PD. Projections of the total resident population by 5-year age groups,
and sex with special age categories: 1999 to 2050. Washington, DC: US Census Bureau; January 13, 2000.

Hollman FW, Mulder TJ, Kallan JE. Methodology and Assumptions for the Population Projections
of the United States: 1999 to 2100. Washington, DC: Population Projections Branch, Population Division,
US Census Bureau, Dept of Commerce; January 13, 2000. Working Paper No. 38.